Electro conductors such as wires, for example, have traditionally and conventionally been used to transmit signal information in many communication types of systems. One major disadvantage of the electrical transmission of signal information in communication systems is, however, that the break in one strand of a multi-element electrically conductive communication line cannot be readily detected. Another equally important disadvantage of the electrical transmission of signal information is the fact that electrical current conductors produce external electric and electromagnetic fields which are a function of the signal currents flowing in the conductors. Such fields may be detected and the signal information discerned external of the conductor and its insulation without disturbing or interrupting the signal current flow in any way. Thus, it is difficult, if not impossible, to provide an entirely "secure" communication system using electrical conduction for the transmission of signal information.
Even the employment of extensive shielding techniques cannot always reduce the external electric and electromagnetic fields below detectable levels to render the transmitted signal information entirely "secure." Another expedient which has been used in the prior art to render electrically conductive communication systems "secure" is to cryptographically encode the signal information. In using cryptographic techniques, however, additional equipments are required including encoding devices at the transmission end of the system and decoding devices at each of the reception points in the system. Thus, shielding and cryptographic encoding techniques involve substantial additional cost as well as a considerable degree of added complication in such systems.
The use of fiber optics for the transmission of signal information in communication systems between sending and receiving terminals has a primary advantage over comparable electrically transmitting systems in that the fiber optics arrangement can provide a relatively simple and "secure" means of transmitting information. Fiber optic cables may be single filament, several filaments, or multi-filaments of several hundred optical fibers. Each fiber is a wholly independent optical waveguide in its operation in that it contains and transmits its signal completely within each fiber and no field of optical energy is produced which may be externally detected or monitored in any way.
Consequently, fiber optic signal information transmission provides a wholly secure system unless one or more of the filaments in a fiber optic cable is ruptured or cut to intercept and detect the signal information being transmitted along the broken fiber.
Accordingly, it is highly desirable that a method and system be provided to detect the rupture of fibers in a fiber optic communication system. Additionally, it is most advantageous that such a method and system for detection of breaks in fiber optic filaments be capable of determining and revealing the location of such a rupture or break in the optical path provided by the fiber optic cable.